From perception to action: Temporal integrative functions of prefrontal and parietal neurons

The dorsolateral prefrontal cortex (DPFC) and the posterior parietal cortex (PPC) are anatomically and functionally interconnected, and have been impl icated in working memory and the preparation for behavioral action. To subs tantiate those functions at the neuronal level, we designed a visuomotor ta sk that dissociated the perceptual and executive aspects of the perception- action cycle in both space and time. In that task, the trial-initiating cue (a color) indicated with different degrees of certainty the direction of t he correct manual response 12 s later. We recorded extracellular activity f rom 258 prefrontal and 223 parietal units in two monkeys performing the tas k. In the DPFC, some units (memory cells) were attuned to the color of the cue, independent of the response-direction it connoted. Their discharge ten ded to diminish in the course of the delay between cue and response. In con trast, few color-related units were found in PPC, and these did not show de creasing patterns of delay activity. Other units in both cortices (set cell s) were attuned to response direction and tended to accelerate their firing in anticipation of the response and in proportion to the predictability of its direction. A third group of units was related to the determinacy of th e act; their firing was attuned to the certainty with which the animal coul d predict the correct response, whatever its direction. Cells of the three types were found closely intermingled histologically. These findings furthe r support and define the role of DPFC in executive functions and in the tem poral closure of the perception-action cycle. The findings also agree with the involvement of PPC in spatial aspects of visuomotor behavior, and add a temporal integrative dimension to that involvement. Together, the results provide physiological evidence for the role of a prefrontal-parietal networ k in the integration of perception with action across time.